libgcc_s.so is broken on powerpc at the moment because 
gcc/gcc/config/rs6000/tramp.asm  expects __PIC__ to be defined when being 
assembled -fPIC. Looking at what other platforms do in gcc/config shows the 
normal gcc inconsistency so where should this get defined (if at all)?

I believe TARGET_OS_CPP_BUILTINS is the right place...

Nick